[PATCH 1/2] arm64: signal: Report signal frame size to userspace via auxv

[Dave Martin]

On Tue, May 08, 2018 at 12:30:44PM +0100, Mark Rutland wrote:
> On Tue, May 08, 2018 at 11:43:30AM +0100, Dave Martin wrote:
> > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> > index fac1c4d..771c7a8 100644
> > --- a/arch/arm64/include/asm/elf.h
> > +++ b/arch/arm64/include/asm/elf.h
> > @@ -24,6 +24,10 @@
> >  #include <asm/ptrace.h>
> >  #include <asm/user.h>
> >  
> > +#ifndef __ASSEMBLY__
> > +#include <asm/processor.h> /* for get_minsigstksz(), used by ARCH_DLINFO */
> > +#endif
> 
> This can live under the existing ifndef __ASSEMBLY__ block, where
> ARCH_DLINFO lives.

Can do.  I don't usually like mixing #includes with the code unless absolutely necessary, but this looks like a pretty trivial case, with just some #defines before the #ifndef __ASSEMBLY__ block.

So I guess this can be moved harmlessly.

> 
> [...]
> 
> > +/*
> > + * Determine the stack space required for guaranteed signal devliery.
> > + * This function is used to populate AT_MINSIGSTKSZ at process startup.
> > + */
> > +int get_minsigstksz(void)
> > +{
> > +	static __read_mostly atomic_t minsigstksz;
> > +
> > +	int ret;
> > +	struct rt_sigframe_user_layout user;
> > +
> > +	ret = atomic_read(&minsigstksz);
> > +	if (ret)
> > +		return ret;
> > +
> > +	init_user_layout(&user);
> > +	ret = setup_sigframe_layout(&user, true);
> > +
> > +	if (ret) {
> > +		WARN_ON(1);
> > +
> > +		ret = SIGSTKSZ;
> > +	} else {
> > +		ret = sigframe_size(&user) +
> > +			round_up(sizeof(struct frame_record), 16) +
> > +			16; /* max alignment padding */
> > +	}
> > +
> > +	/*
> > +	 * The computed value (ret) is invariant, so its value can be
> > +	 * safely stored irrespective of whether some other racing
> > +	 * task got there first:
> > +	 */
> > +	atomic_set(&minsigstksz, ret);
> > +	return ret;
> > +}
> 
> Can we set up minsigstksz at some initcall time? that way get_minstksz()
> can return minsigstksz with no conditionality at all.

I would have preferred to do that, but I wasn't sure where to put it.

Unless arch_initcall_sync() works for this, I don't know what to
suggest.

Cheers
---Dave